The present invention relates to a heating device. More particularly the present invention relates to a heating device which has a heating circuit connected to the hydraulic circuit of an internal combustion engine, a delivery pump operated by an electric motor and formed as a flow pump driven by the electric motor via a magnet coupling. Such a device in which the delivery element is arranged so as to be fixed in proximity to the suction opening as seen in the direction of its axis of rotation--specifically for reasons of the efficiency of the pump--is already commercially available. In certain operating states of the heating device the cooling water pump can produce full delivery capacity while the delivery pump located in the heating circuit is stopped. When the heating circuit cannot be separated from the coolant circuit the medium flow produced by the coolant pump flows through the pump of the heating circuit. In so doing the heating circuit pump is then also driven by the medium flowing through it, although the electric motor is stopped. The magnetic coupling between the pump and drive motor is accordingly broken. But it is then impossible to couple the two coupling halves when starting the electric motor subsequently. To bring about a coupling between the two coupling halves, the internal combustion engine and the electric motor would first have to be switched off. But since this defect can also occur when the electric motor is running there is a so-called "overflowing" of the heating circuit pump. This is possible because the delivery quantity of the coolant circuit pump considerably exceeds that of the pump in the heating circuit.